Pressure loss and linearity law of phase change in liquid nitrogen seepage flow in coal mine goaf

WU Xue; CHEN Shiqiang; CHEN Fangxing; LIU Gang; ZHAO Pengtao

doi:10.13225/j.cnki.jccs.2024.1030

Abstract：Spontaneous combustion of coal in goaf areas is one of the thermal dynamic disasters.A bottleneck in prevent-ing and controlling spontaneous combustion of residual coal is precise fire prevention and extinguishing,with one of the scientific issues being the loss of liquid nitrogen flow and its rapid prediction method within coal mine goaf.Based on the structure of the porous medium in coal mine goaf,an experimental platform for liquid nitrogen seepage,phase change,and pressure loss was constructed.Low-temperature-resistant calcium-sodium glass was selected to form porous medium chan-nels,through which studies were conducted on the effects of seepage velocity and particle size on the pressure loss during the phase change of liquid nitrogen in the porous medium.Numerical simulations were further utilized to validate and ex-pand the data sets on the influence of seepage velocity on pressure loss.The results indicate that when liquid nitrogen seeps through the porous medium conduit,due to gravity and vaporization effects,a stratified wetting phenomenon occurs on the outer wall of the low-temperature conduit.Secondly,as the particle size used to fill the porous medium experiment-al platform increases from 3 mm to 6 mm,and the porosity changes from 0.240 9 to 0.266 9,the liquid nitrogen undergoes phase change to gaseous nitrogen within the porous medium channel,resulting in increased volume and pressure.Under conditions where fluid density,viscosity,and surface tension remain constant,with increasing seepage velocity,capillary forces and viscous forces interact at the gas-liquid interface,causing the fluid to transition from a Newtonian to a non-Newtonian fluid,which leads to a linear relationship between pressure loss per unit length and seepage velocity.In addi-tion,the relative error between the numerical simulation model's computational results and the experimental data does not exceed 15％,and when the seepage velocity of liquid nitrogen increases from 0.001 m/s to 0.08 m/s,the linearity fit between pressure loss per unit length and seepage velocity reaches 99％,further validating the reliability of the experi-mental conclusions.The findings reveal the linear variation pattern between pressure loss during the phase change of li-quid nitrogen in the porous medium and seepage velocity,providing a theoretical basis for precise fire prevention and ex-tinguishing in coal mine goaf.